[gdal-dev] BAG CRS

Fri Apr 22 09:35:37 PDT 2022

Sorry Even,

I should have done more research on my end up front before sending this. A client told us his WKT 2.0 BAG was created with GDAL. Looking at it some more, it was the vertical CRS that was WKT 2.0.

Their vertical CRS looked as follows:
<gco:CharacterString>VERTCRS["ellipse",VDATUM["NAD83(2011) / UTM zone 10N + ellipse"],CS[vertical,1],AXIS["ellipsoid height (h)",up,LENGTHUNIT["metre",1]]]</gco:CharacterString>

Cheers,
André

From: Even Rouault <even.rouault at spatialys.com>
Sent: April 22, 2022 13:22
To: Vautour, André (INT) <Andre.Vautour at Teledyne.com>; gdal-dev at lists.osgeo.org
Subject: Re: [gdal-dev] BAG CRS

External Email

André,

I don't confirm this trying:

$ gdal_translate autotest/gcore/data/byte.tif byte.bag

$ gdalinfo byte.bag -mdd xml:BAG | grep PROJCS
            <gco:CharacterString>PROJCS["NAD27 / UTM zone 11N",GEOGCS["NAD27",DATUM["North_American_Datum_1927",SPHEROID["Clarke 1866",6378206.4,294.978698213898,AUTHORITY["EPSG","7008"]],AUTHORITY["EPSG","6267"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4267"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-117],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH],AUTHORITY["EPSG","26711"]]</gco:CharacterString>

This is WKT1

I'm wondering if the confusion might come from looking at the CRS reported by gdalinfo, which will always be WKT2 in recent GDAL versions whatever the encoding in the source dataset itself ?

Or perhaps you try to write a Geographic 3D CRS ? in which case WKT2 will be used since there's no WKT1 representation for this

$ gdalwarp -overwrite autotest/gcore/data/byte.tif byte.bag -t_srs EPSG:4979 -ot float32

$ gdalinfo byte.bag -mdd xml:BAG | grep GEOGCRS
            <gco:CharacterString>GEOGCRS["WGS 84",ENSEMBLE["World Geodetic System 1984 ensemble",MEMBER["World Geodetic System 1984 (Transit)"],MEMBER["World Geodetic System 1984 (G730)"],MEMBER["World Geodetic System 1984 (G873)"],MEMBER["World Geodetic System 1984 (G1150)"],MEMBER["World Geodetic System 1984 (G1674)"],MEMBER["World Geodetic System 1984 (G1762)"],MEMBER["World Geodetic System 1984 (G2139)"],ELLIPSOID["WGS 84",6378137,298.257223563,LENGTHUNIT["metre",1]],ENSEMBLEACCURACY[2.0]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433]],CS[ellipsoidal,3],AXIS["geodetic latitude (Lat)",north,ORDER[1],ANGLEUNIT["degree",0.0174532925199433]],AXIS["geodetic longitude (Lon)",east,ORDER[2],ANGLEUNIT["degree",0.0174532925199433]],AXIS["ellipsoidal height (h)",up,ORDER[3],LENGTHUNIT["metre",1]], [... snip ....] ,ID["EPSG",4979]]</gco:CharacterString>

(I see that gdalinfo also issues a "ERROR 1: PROJ: proj_create_compound_crs: components of the compound CRS do not belong to one of the allowed combinations of http://docs.opengeospatial.org/as/18-005r4/18-005r4.html#34" when reading this, which I suspect comes from the fact that it tries to create a CompoundCRS from this 3D GeogCRS and the "VERT_CS["unknown", VERT_DATUM["unknown", 2000]]", so writing 3D GeogCRS isn't really appropriate for BAG)

Even
Le 22/04/2022 à 18:01, Vautour, André (INT) a écrit :
Hi all,

It has just come to my attention that the BAG driver in GDAL is writing the CRS with a WKT codeSpace and a WKT 2.0 string as the code. While I am fairly sure we started that incorrect practice here at CARIS with a WKT 1.0 string, this is the first time I’ve seen a WKT 2.0 string written in there, and I am therefore concerned about interoperability.

I think we can all agree that what makes the most sense is to write an EPSG codebase with the EPSG code if we have it, and I think falling back to a WKT 1.0 string if it is not EPSG is a reasonable fallback if it is not EPSG, given how it has been used in the past, but I am worried that older software won’t recognize the WKT 2.0 string.

Would you be willing to take a pull request that does that? Worst-case, would you be fine with changing that WKT 2.0 string to a WKT 1.0 string?

Regards,
André

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